Re: gnus-cloud work

[Ted Zlatanov <tzz@lifelogs.com>]

On Fri, 01 Jul 2016 21:00:27 -0400 Ted Zlatanov <tzz@lifelogs.com> wrote: 

TZ> Update:
TZ> * newsrc data format changed, new entries have type :newsrc-data and the
TZ>   contents are inlined

TZ> * `M-x gnus-cloud-upload-all-data' will upload all the data, files and
TZ>   newsrc both

TZ> * (this must be run manually for now) `M-: (gnus-cloud-download-data t 1)'
TZ>   will get all the download data and install the newsrc and file data

TZ> Only full uploads/downloads work.

TZ> This is worth another test if people are adventurous, but *make sure you
TZ> back up your newsrc.eld* before downloading the data.

I made a few more tweaks:

* only update if data is newer (can be overriden)
* add `gnus-cloud-interactive' variable to confirm updates (good for testing and paranoia)

The last piece missing is where to hook the upload and download code.

Upload could happen every 30 minutes or every time more than 10 groups
are updated? We have to be careful of race conditions where two machines
are not aware that the other has uploaded "locally newer" data. But
maybe that's OK, if we agree that the typical use case is one user on
multiple machines, not multiple users on multiple machines.

Download... not sure... maybe every time Gnus refreshes all groups with `g'?

Or maybe a background process could continuously monitor IMAP for new
articles in the cloud group? I don't know how that would work from the
Gnus side, but it would be super nice for the user. Any IMAP/nnimap experts?

Finally, currently the sequence number is a local number. Each machine
starts from 1 and walks up to the global max sequence (from the IMAP
articles). I think that's not ideal, because two machines can easily end
up uploading with the same sequence number without careful
synchronization. Global counters are hard to implement. Maybe it's
better to simply use a timestamp string or the raw IMAP article number
as the sequence number. The IMAP article number sequence in particular
is guaranteed by the IMAP server, so I'm leaning towards that. What do
you think?

Once upload, download, and sequence numbers are settled, I'll squash all
the commits and merge this into Emacs master branch.

Ted